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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

388

FATTY SUBSTANCES  (GENERAL METHODS)

19. Unsaponifiable Substances

By unsaponifiable substances in fatty matters is usually meant both
substances which are not attacked by the alkali during the saponification,
such as mineral oils, resin oils, solid paraffin and ceresine—which are un-
saponifiable in the strict meaning of the term—and also substances which
are liberated by the saponification itself and separate owing to their slight
solubility under the conditions of saponification, such being, for instance,
the higher alcohols (ceryl and myricyl alcohols, cholesterol and phytosterol).

The latter substances form an integral part, i.e., enter into the con-
stitution, of many fatty matters and waxes, while the former (mineral oils
and the like) may be added artificially to fats.

To separate the unsaponifiable substances from fats it suffices to saponify
in the usual way (see 5), to dissolve the soap in water and shake the solution
with ether or petroleum ether (b.pt. below 80°), to separate the two liquids
and evaporate the ethereal solution, which will leave the unsaponifiable
matters. To prevent emulsification, which often occurs when an alkali
soap is shaken with ether, a little alcohol may be added and a larger quantity
of ether used.

To determine quantitatively the unsaponifiable substances, it is more
convenient and accurate to work as follows:

20 grams of the substance to be examined are saponified by
boiling with 15 c.c. of 50% caustic soda solution and 50 c.c. of 95% alcohol
for about 30 minutes, the liquid being then transferred to a dish and the
alcohol evaporated, 8-10 grams of sodium bicarbonate (to transform the
excess of caustic alkali into carbonate) and 70-80 grams of siliceous sand
being gradually mixed in. When the whole is quite dry it is placed in a
thick filter-paper thimble and extracted in an extraction apparatus with
petroleum ether (b.pt. below 80°). The solvent is subsequently extracted,
the residue, dried at 100° and weighed, giving the quantity of unsaponifiable
matter.

The unsaponifiable matters which may be extracted from fats in this
way or by the other methods given under particular cases (see Tallow, 3,
Detection of Phytosterol) are mainly as follows:

1. Higher Alcohols.—These are divided into those of the aliphatic
series (cetyl, ceryl, myricyl) and those of the aromatic series (cholesterol,
phytosterol). The former, which occur especially in waxes, are solid and
melt at moderately high temperatures—cetyl alcohol at 50°, ceryl at 79°
and myricyl at 85°; they are soluble in alcohol, from which they crystallise
readily, and they dissolve in and combine with boiling acetic anhydride,
the solution remaining liquid on cooling provided that a sufficient excess
of acetic anhydride were used.

The aromatic higher alcohols are found in almost all fats, although often
in very small proportions.

Cholesterol occurs in fats of animal origin. It is soluble in hot alcohol,
from which it crystallises, on cooling, in nacreous leaflets having the appear-
ance of rhombic plates under the microscope (Fig. 54). It melts at 145-150°
and dissolves in boiling acetic anhydride, the cold solution depositing aic methods for the quantitative separation of the solid